Satellite Positioning System (SPS) receivers, such as receivers for the Global Positioning System and for the Global Orbiting Navigational System discussed below, are now used for many applications requiring determination of the observer's location anywhere on or in the vicinity of the Earth.
An SPS receiver includes an SPS antenna to receive the SPS signals transmitted from one or more SPS satellites, an SPS processor to calculate the SPS antenna's position and time of observation of that position from the SPS signals, a display processor to convert the SPS position and observation time into information that is useful for an application, and a display to show the information to the user. The SPS antenna must be positioned with a direct line of sight to the SPS satellite or satellites from which the receiver receives SPS signals.
Current SPS receivers adopt one of two formats. The first format, commonly called "handheld," includes an SPS antenna, an SPS processor, a display processor, and a display in a single unit. A problem with this format is that the user must remain in the open to preserve a direct line of sight from the SPS antenna to one or more SPS satellites while operating and observing the user's display.
The second format places the SPS antenna in an antenna unit and the display in a separate display unit. The SPS processor and the display processor may be contained in the antenna unit, in the display unit, or in a separate unit or units. In this second format, a cable is used to connect the GPS antenna unit to the display unit, and to any unit(s) containing the SPS processor and the display processor. This format allows the user to separate the SPS antenna and the display so that the SPS position and time information can be observed and operated upon in a protected environment. However, the cable and its connections are inconvenient to use when an observer moves around within a region. Further, the cable and its connections are expensive and prone to breakage or malfunction.
Workers in other technical areas have developed some technology that is relevant here. Yokoyama et al, in U.S. Pat. No. 4,641,366, disclose use of portable radio (handset) apparatus, including first and second antennas recessed into one side of the portable radio and capable of receiving signals in two separate frequency bands to which the radio responds. The radio apparatus includes one or two frequency converters to convert between audio and rf frequencies.
A small, handheld antenna is disclosed in U.S. Pat. No. 4,701,763, issued to Yamamoto et al. FIG. 14 of this patent illustrates application of this antenna concept to an rf signal receiver or transmitter. The high gain antenna is small enough to be insertable into many types of signal-receiving electronics devices, such as pagers. Most of this disclosure is concerned with the three-layer structure of the antenna.
Fowler, in U.S. Pat. No. 4,754,283, discloses a cordless GPS sounding device using two antennas, a first antenna to receive radiowaves from an antenna carried by a balloon aloft that indicates wind direction and velocity, and a second antenna to receive conventional GPS signals from a GPS satellite. The ground-based GPS signal receiver and antenna are connected by cables or wires to the balloon-sensing antenna and to a computer for determining wind direction and velocity as the balloon drifts relative to the receiver
Blaese discloses a portable antenna suitable for mounting on a motor vehicle's side window, in U.S. Pat. No. 4,804,969. The mounting means facilitates easy installation and removal. The antenna apparatus includes a pivotable or fold-out, current feed line radiator, which is mounted on the outside surface of the window and is electrically attached to other portions of the antenna electronics located on the inside surface of the window. A coaxial cable connects the inside surface electronics to a separate transceiver located inside the vehicle. The line radiator includes a 5/8 wavelength radiator, stacked on a helical separation coil, stacked on a 3/8 wavelength radiator, for field cancellation purposes. Blaese discloses a cordless, easy-mount antenna of similar design that obviates the need for the coaxial cable, in U.S. Pat. No. 5,059,971; a second line radiator provides a wireless link with the transceiver.
A very thin radio housing having a printed circuit loop antenna mounted in a plane on an interior wall of the housing is disclosed by Urbish et al in U.S. Pat. No. 4,894,663. The housing opens as a notebook would open, to disclose the antenna and a portion of the antenna electronics, and a portion of the antenna circuit is located on a hinge that facilitates opening and closing the housing. The integrated antenna, electronics and housing is intended to serve as a credit card size page signal receiver or other signal receiving system.
Newland discloses a small antenna for a cordless telephone in U.S. Pat. No. 4,897,863. The tip-and-ring wiring in the associated telephone handset serves as the antenna, which provides telecommunication capability with the :rest of the world through a wireless link to inside telephone wiring in an adjacent structure, such as a home. The tip-and-ting wiring thus serves as both a signal feed line and as an antenna. Audio and radio frequency signals can be transmitted and received using this antenna.
Mori et al, in U.S. Pat. No. 4,935,745, disclose a credit card size radio receiver with a slot antenna integrated as part of the receiver housing. Three contiguous sides of the card size housing together serve as the antenna. An rf frequency circuit (not shown) receives and processes the incoming radio signals and is carried by the housing. The apparatus is intended to serve as a card size page signal receiver.
U.S. Pat. No. 5,052,645, issued to Hixon, discloses a telescoping pole antenna that can be used to support a GPS signal antenna. The pole includes many concentric telescoping, vertically oriented cylinders that can be collapsed to one meter in height or extended to a height of as much as 20 meters. The antenna and telescoping support pole combination is not portable and would probably have a mass of several tens of kilograms.
A credit card size radio page signal receiver, with a portion of the receiver housing serving as an antenna, is disclosed in U.S. Pat. No. 5,054,120, issued to Ushiyama et al. Top and bottom walls of the housing serve as part of a loop antenna that can handle VHF signals. The antenna is not defined by any particular circuit integrated with the housing.
Raubenheimer et al disclose a handheld navigational aid, including a keyboard for data entry, a visual display and a loudspeaker for audible communication, in U.S. Pat. No. 5,059,970. The visual display presents a small map of a chosen region, and the map provides two cursors to indicate and determine the distance between two points on the map. An icon indicates the position of a chosen marine or airborne vessel on the map, and present position relative to a fixed reference point is visually displayed as distance/bearing or as latitude/longitude coordinates in a two-dimensional representation. The apparatus contains a microprocessor and stored-on-board algorithms and mathematical equations for signal processing purposes and relies upon a resettable internal clock for certain display purposes. Input signals appear to be entered through the keyboard.
What is needed is "cordless" SPS apparatus that allows the user: to place the SPS antenna in a direct line of sight from one or more SPS satellites; to operate and observe the position and/or observation time display in a protected environment; and to allow the user and display unit to move around without the inconvenience and poor reliability associated with use of a cable.